Apparatus for use in crystal pulling

Abstract

An apparatus for pulling a monocrystalline ingot from a semiconductor source material located within a growth chamber as the ingot is grown on a seed crystal according to the Czochralski method. The apparatus comprises a drum, a chuck constructed for holding the seed crystal and the ingot, and a cable having a first end connected to the drum, a second end connected to the chuck and a portion wound around the drum. The portion of the cable wound around the drum exerts a normal force on a circumferential surface of the drum corresponding to the tension in the cable. The drum and cable interact to produce a friction force resisting sliding movement of the cable relative to the drum in a direction lengthwise of the cable. The drum is capable of unwinding cable from the drum thereby to let out the cable and lower the chuck, and capable of winding the cable around the drum thereby to reel in the cable and draw the chuck upwardly. The chuck has a mass selected to exert a pre-tension on the cable prior to growing the ingot such that the increase in the friction on the portion of the cable wound around the drum as the cable is reeled in to pull the ingot from the source material is at least equal to the increase of the weight of the ingot as it grows on the seed crystal from the molten source material.

What is claimed is: 
     
       1. An apparatus for pulling a monocrystalline ingot from a semiconductor source material located within a growth chamber as the ingot is grown on a seed crystal according to the Czochralski method, the apparatus comprising: a drum mounted for rotation about an axis;   a chuck constructed for holding the seed crystal and the ingot grown on the seed crystal from the source material; and   a cable having a first end connected to the drum, a second end connected to the chuck and a portion wound around the drum, the portion of the cable wound around the drum exerting a normal force on a circumferential surface of the drum corresponding to the tension in the cable, the drum and cable interacting to produce a friction force resisting sliding movement of the cable relative to the drum in a direction lengthwise of the cable, the drum being capable upon rotation in a first direction of unwinding cable from the drum thereby to let out the cable and lower the chuck, and capable upon rotation in a second direction opposite the first direction of winding more of the cable around the drum thereby to reel in the cable and draw the chuck upwardly;   the chuck having a mass selected to exert a pre-tension on the cable prior to growing the ingot such that the increase in the friction on the portion of the cable wound around the drum as the cable is reeled in to pull the ingot from the source material is at least equal to the increase of the weight of the ingot as it grows on the seed crystal from the molten source material whereby the cable does not slip on the drum as the ingot is grown.   
     
     
       2. An apparatus as set forth in claim 1 wherein the mass of the chuck is at least equal to:   R*(dM/dL)/μ     wherein: R=radius of the drum;   dM/dL=rate of increase in the mass of the ingot per change in length of the cable, the length of the cable being defined as a vertical distance between an upper end of the chuck and a point of contact between the cable and drum; and   μ=static coefficient of friction between the cable and drum.     
     
     
       3. An apparatus as set forth in claim 2 wherein the chuck comprises a lower end having an opening therein for receiving a portion of the seed crystal, an upper end having an opening for receiving the cable, and a central portion, the apparatus further comprising a weight receivable on the central portion for increasing the mass of the chuck. 
     
     
       4. An apparatus as set forth in claim 3 wherein the chuck further comprises a stem extending through the central portion of the chuck and wherein the weight comprises a ring sized and shaped for placement on the stem. 
     
     
       5. An apparatus as set forth in claim 4 wherein the weight comprises plural rings. 
     
     
       6. An apparatus as set forth in claim 4 wherein the ring is formed from a refractory metal. 
     
     
       7. An apparatus as set forth in claim 4 further comprising a shield for covering the ring. 
     
     
       8. An apparatus as set forth in claim 7 wherein the shield is formed from graphite. 
     
     
       9. An apparatus as set forth in claim 1 wherein the drum has a groove formed in the circumference thereof, the portion of the cable being disposed within the groove. 
     
     
       10. An apparatus as set forth in claim 9 wherein the surface of the groove has a friction enhancing coating to increase the static coefficient of friction between the cable and the drum. 
     
     
       11. An apparatus as set forth in claim 10 wherein the friction coating is selected from a group including a plasma spray tungsten carbide coating and a plasma spray chromium coating. 
     
     
       12. An apparatus as set forth in claim 9 wherein the groove is defined by diverging side walls which form a generally V-shaped groove. 
     
     
       13. An apparatus as set forth in claim 12 wherein the mass of the chuck is at least equal to:   R*(dM/dL)*(sin (α/2))/μ     wherein: R=radius of the drum;   dM/dL=rate of increase in the mass of the ingot per change in length of the cable, the length of cable being defined as a vertical distance between an upper end of the chuck and a point of contact between the cable and drum;   α=angle between the side walls of the groove;   μ=static coefficient of friction between the cable and the drum.     
     
     
       14. An apparatus for pulling a monocrystalline ingot from a semiconductor source material located within a growth chamber as the ingot is grown on a seed crystal according to the Czochralski method, the apparatus comprising: a drum mounted for rotation about an axis;   a chuck constructed for holding the seed crystal and the ingot grown on the seed crystal from the source material; and   a cable having a first end connected to the drum, a second end connected to the chuck and a portion wound around the drum, the portion of the cable wound around the drum exerting a normal force on a circumferential surface of the drum corresponding to the tension in the cable, the drum and cable interacting to produce a friction force resisting sliding movement of the cable relative to the drum in a direction lengthwise of the cable, the drum being capable upon rotation in a first direction of unwinding cable from the drum thereby to let out the cable and lower the chuck, and capable upon rotation in a second direction opposite the first direction of winding more of the cable around the drum thereby to reel in the cable and draw the chuck upwardly;   at least a portion of a surface of the drum in contact with the cable having a surface finish providing an increase in friction between the cable and the drum as the cable is reeled in to pull the ingot from the source material which is at least equal to the increase of the weight of the ingot as it grows on the seed crystal from the molten source material whereby the cable does not slip on the drum as the ingot is grown.   
     
     
       15. An apparatus as set forth in claim 14 wherein the drum has a groove formed in the circumference thereof, the portion of the cable being disposed within the groove. 
     
     
       16. An apparatus as set forth in claim 15 wherein the groove is defined by diverging side walls which form a generally V-shaped groove. 
     
     
       17. An apparatus as set forth in claim 15 wherein the surface of the groove has a friction enhancing coating to increase the static coefficient of friction between the cable and the drum. 
     
     
       18. An apparatus as set forth in claim 17 wherein the friction coating is selected from a group including a plasma spray tungsten carbide coating and a plasma spray chromium carbide coating. 
     
     
       19. An apparatus as set forth in claim 14 wherein the mass of the chuck is at least equal to:   R*(dM/dL)/μ     wherein: R=radius of the drum;   dM/dL=rate of increase in the mass of the ingot per change in length of the cable, the length of the cable being defined as a vertical distance between an upper end of the chuck and a point of contact between the cable and drum; and   μ=static coefficient of friction between the cable and drum.